10.11.Â xxx_isa_shutdown

This routine is called when the system is about to be shut
down. It is expected to bring the hardware to some
consistent state. For most of the ISA devices no special
action is required, so the function is not really necessary
because the device will be re-initialized on reboot
anyway. But some devices have to be shut down with a special
procedure, to make sure that they will be properly detected
after soft reboot (this is especially true for many devices
with proprietary identification protocols). In any case
disabling DMA and interrupts in the device registers and
stopping any ongoing transfers is a good idea. The exact
action depends on the hardware, so we do not consider it here
in any detail.